1. Field of the Invention
The invention relates to a ball screw and an electric power steering system including the ball screw.
2. Description of the Related Art
A conventional ball screw includes a ball screw shaft, a ball nut, a plurality of balls, and a rolling path. The plurality of balls moves in the rolling path as the ball nut rotates with respect to the ball screw shaft. Japanese Patent Application Publication No. 2002-276765 (JP 2002-276765 A) discloses an example of the conventional ball screw.
In the conventional ball screw, when a load acts on the ball screw shaft, flexural deformation of the ball screw shaft is caused. At this time, magnitudes of the loads that are applied to the respective balls are different from each other. In the ball screw described in JP 2002-276765 A, no consideration is given to that the loads with different magnitudes are applied to the respective balls due to the flexural deformation of the ball screw shaft. Therefore, in the ball screw, a large load may be applied to a part of the plurality of balls.